Common Faults in Three-Roll Plate Bending Machines

I. Rolling Quality Faults

Poor Cylinder Roundness / Ovality: Usually caused by parallelism deviation between the upper and lower rolls, or asymmetric positioning of the side rolls, leading to uneven force distribution on the plate. This can be resolved by calibrating roll shaft parallelism with a dial indicator, and applying local corrections using curved backing plates or ring fixtures.

Over-rolling (Excessive Curvature): Press the emergency stop immediately, raise the upper roll by 2-3mm to release pressure, and slowly release the material stress by rolling back 15° in three separate passes. Allow a springback margin of 0.8%-1.2% for subsequent operations.

Excessive Flat Edges: An inherent characteristic of symmetrical three-roll bending machines. This can be solved by pre-bending the plate ends in advance, or by upgrading to asymmetrical or fully hydraulic models with pre-bending capabilities.

Workpiece Deviation (Skewing): Occurs when the plate is not fed parallel to the roll axis. Reposition the plate to ensure the feed direction is perfectly perpendicular to the roll axis.

II. Mechanical Faults

Excessive Temperature Rise in Bearing Housings: Caused by insufficient lubrication, bearing wear, or overload. Stop the machine to apply grease, check bearing clearances, and avoid overloading the equipment.

Severe Vibration / Abnormal Noise: Indicates damaged roll bearings or excessive backlash in the transmission gears. Stop the machine, disassemble the gearbox, replace worn bearings, and adjust the gear meshing clearance.

Roll Shaft Jamming: Caused by metal chips embedded in the roll surface or jammed transmission chains/gears. Clear foreign objects from the roll surface and inspect the transmission components for proper lubrication and wear.

Tilting Mechanism Failure: Triggered when the tilting mechanism is activated before the workpiece completely clears the upper roll. Strictly follow operating procedures; only operate the tilting beam after the workpiece has fully disengaged from the rolls.

III. Hydraulic System Faults

Insufficient System Pressure / Inability to Drive Load: Caused by internal leakage from a worn hydraulic pump or a stuck pressure relief valve. Clean the relief valve, inspect the hydraulic pump for wear, and replace contaminated hydraulic oil and filters.

High Oil Temperature / Equipment Overheating: Caused by a clogged cooler or prolonged system relief. Clean dirt and oil from the cooler, check the relief valve's working condition, and avoid prolonged full-load operation.

Hydraulic System Leakage: Caused by aged/damaged seals or loose pipe fittings. Replace aged seals, tighten loose fittings, and regularly check the hydraulic oil level.

Cylinder Creeping / Stuttering Motion: Caused by air trapped in the hydraulic system or aged seals. Bleed the system to remove air and replace the aged cylinder seals.

IV. Electrical Control Faults

System Fails to Return to Home Position: Caused by a lost zero-pulse signal or a damaged position measurement component. Use an oscilloscope to check the zero-pulse signal and replace the faulty measurement sensor.

System Alarms / Position Loop Hardware Faults: Caused by electrical interference. Connect filter capacitors in parallel to the affected circuit to eliminate interference, and inspect the cable shielding for integrity.

Abnormal PLC Interface Signals: Interface signals do not match the manual's standard values. Access the interrupt buffer via the PLC and refer to the interface manual to quickly locate the fault.

Oil Pump Fails to Start / No Machine Action: Caused by an open circuit in the electrical control loop or a tripped thermal relay. Check the power supply circuit and the thermal relay status, reset the protective device, and restart the equipment.

V. Emergency Stop Faults

If any of the following situations occur, the power must be cut off immediately for maintenance. Operations may only resume after the hazard has been eliminated:

The bearing housing temperature exceeds 60°C, showing signs of overheating or smoking.

White smoke is emitted during equipment operation.

The entire machine experiences severe and continuous vibration.

Noise suddenly increases significantly, accompanied by abnormal metallic clashing sounds.